Method of copying



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3,103,881 METHOD OF COPYING Emil W. Grieshaber, White Bear Lake, Min toM nnesota Mining 8: Manufacturing Company, St. Paul, Mmm, a corporationof Delaware Filed Oct. 20, 1958, Ser. No. 768,008

3 Claims. (Cl. 101-4493) This invention relates to the thermographicreproduction of graphic originals. {In one significant aspect itprovides for the visible reproduction on untreated paper or otherreceptor surfaces of printed or other graphic origmals, eitherblack-and-white or colored, bylmethods in- U i ed States P e 595 9?volving brief intense irradiation of the graphic subjectmatter. Inanother aspect the invention provides for the preparation, by simpleirradiation, of intermediate reproductions of graphic originals, fromwhich duplicates may subsequently be produced by known techniques. Theinvention also provides novel sheet materials in the form ofheat-sensitive copy-sheets having application in the. attainmentresults.

. The reproduction of typewritten or printed-documents 'or otherg-raphicoriginals by thermographic methods has recentlybecome of widespreadcommercial importance. One method involves subjecting the printedsurface to brief intense irradiatiom'for example from a heated tung-.

sten filament, through" a transparent heahsensitive copysheet held inheat-conductive contact against, said surface. 'j The resultingselective heating effect at the inked areas causes a visible'ohange tooccur in corresponding areas of the heat-sensitive sheet, thus-producingthe desired repro- Patented Sept. 17, 1963 Exemplary materials employedand procedural details specific followed will now be further set forthin terms of illustrative but non-limitative examples.

. Example 1 An intermediate heat-senstive copy-sheet is first prepared,using as a flexible backing or support web a one-- mil orientedpolyester film, such for example as Mylar polyester film. The web iscoated on one surface with a three-mil uniform layer of a liquid coatingcomposition,

and dried at room temperature. The formulation of the coatingcomposition is as follows, proportions being given in parts by weight:

Ferric stearate 192 Spiroindane Ethyl cellulose j 91 Triphenyl phosphate29 Acetone 1 1 527 flheferric stearatejs ground, with a portion of theethyl of these and other. useful and advantageous cellulose and-acetonem persion is obtai ,a ball mill until a smooth disnd for 72 hours an aonelpjnt-v capacity mill two-thirds 'c stearate is thereby reduced to aminimum particle siie, no further reduction observable on microscopicexamination being obtained on further grinding.

' The spiroindaneemployed is a polyhydrox y phenol and is apolymericfreacftion product of acetone and pyrogallol formed by reactionat approximately room temperature in the presence of phosphorusoxychloride catalyst, hav-.

duction. The process is ordinarily carried out with radiation' high ininfra-red, and is most effectivewithblackand-whiteoriginals, the carbonof theink being highly absorptive of infra-red. Colored inks areabsorptive of other radiation, and sources are known which provideadequate intensity "of such radiation to produce the de-' 4 siredselective heating'eifect with colored image areas also. It has beenfound, however,-that many heat-sensitive' copy-sheets which are fullyeffective with black-andwhite originals do not produce efiectivere'productions'of images printed in colored inks. Again, the unchangedareas of the exposed copy-sheet remain sensitive wheat and hence a copyproduced on such sheet may be overprinted' or otherwise altered. Thus,although thermographic copying procedures otter rapid and convenientreproduction of graphic originals, and'avoid such prior tion' whichisthen' mixed with the ferric 'stearate disperart requirements asprotection from light-exposure, or solution or. fume image-development,and'hencd'have become commercially widely adopted, they have not thusfar been found. fully effective for specific applications.

The present invention offers means for enlarging the scope ofthermographic copying inthe respects hereinbefore indicated as well asin other ways, as will hereinafter become apparent or will bespecifically pointed out. Clear and sharp reproduction of graphicoriginals having colored as well-as black image areas is providedf Thereproduction may be obtained on untreated support members such as paper,glass, plastics, fabric, Wood,- metal,

and various other materials. The reproductions may in some instances befurther employed in the production of additional duplicates- I e Theseand other advantages are-attained, in accordance with the principles ofthis invention, by a two-stage irradiation procedure in which athermographic reproduction of the graphic original is first produced onan intermediate heat-sensitivecopy-sheet by an initial irradiation, andthe visibly altered image-forming portions thus provided are thentransferred to a white paper or other receptor sheet by a furtherirradiation, preferably at a higher intensity.

ing a moderately high molecularweight of about 1 900-16 00; meltingwithin approximately the range. 220-230 C., and ctnn'pletely soluble inacetone. It is combined with the triphenylphosphate .and the remainingprinting apparatus having as the supportfor the original and copy-sheeta transparent glass cylinder with an outside dameter of 1% inches. A gasflash tube with a uniform internal diameter of 2 mm. is supportedwithin'and along the axis of said tube. The flash tube is filled withXenon under a pressure of 600 mm. Hg -and contains two electrodes spaced10 inches apart and enclosed in suitable terminal bulbs. The lamp isactuated from a capacitor having a capacity of mfd. which may be chargedat any desired voltage. Means for initiating the discharge through thelamp are also provided. Other specific dimensions are equallyapplicable, but those given here have proven useful in practice andfurther description will therefore for convenience be in terms of suchlamp system.

The heat-sensitive coated film is wrapped around the glass cylinder withthe polyester surface towardthe glass. The printed original is thenplaced over the'filrn and with the printed surface, of which a copy isdesired, in contact with the outwardly positioned sensitive coating. Afurther wrapping of conformable film, fabric or the like may be employedto hold theoriginal and copy-paper together under pressure. Thecapacitor is then charged to about 2300 volts and discharged throughtheflash tube,

Typically, a 200 gram-charge is,

For this purpose there is preferably employed a thermographic producingan intense brief irradiation of the composite of paper and filrn. Theresulting heating of inked areas of the graphic original producesheating and darkening of corresponding portions of the heat-sensitivecoating. The background areas remain unchanged.

The printed page or other graphic original is next removed and replacedby a sheet of plain white paper, and the irradiation is repeated, inthis case at a voltage of about 2800. The previously unaffectedbackground areas of the copy-paper are now found to be drasticallydarkened but to remain affixed to the support film. The previouslydarkened image portions of, the heat-sensitive layer are found at thesame time to be substantially completely transferred to the white paper,forming a permanent reproduction of the graphic original on the paperand a corresponding negative transparency in the copy-sheet.

Formation of the image areas in the heat-sensitive surface may beaccomplished in the apparatus described at light intensitiesand exposuretimes obtained at voltages in the approximate range of 2000-3000 volts,and transfer of image likewise may be accomplished within the range ofabout 2500-3500 volts. Howeverit is necessary that the irradiationemployed for imagetransfer be at least as intense as that used in makingthe intermediate copy, if effective transfer is to be attained.

The amount of phenol (spiroindane) employed in the coating compositionof Example 1' is much less than the amount required for optimumdarkening of the composition and which would normally be employedinheatsensitive copy-papers using these reactants, being only about 35-40%of said optimum amount. Surprisingly, it is found that this decrease inphenol component results in an increase rather than a decrease in theoptical density of the resulting copy when transferred to the whitepaper. This result is due to the substantially complete transfer of thecoating containing the reduced amount of phenol, as compared to thelimited transfer occurring at the higher proportions. 7

Effective transfer of the image portions is likewise improved byselection of low molecular weight ethyl cellulose or other binder, carebeing taken to avoid the stickiness encountered with certain classes'ofpolymeric binders at the very low molecular weight levels.

The degree of milling of the ferric stearate is not particularlycritical for copy-papers designed for reproduction from black-onwhiteoriginals. In the foregoing'example, effective reproductions of suchoriginals have been produced with compositions prepared with only 6-12hours of grinding in the ball mill. The reproduction of originalsprinted in colored inks requires somewhat higher intensity radiation,and under these conditions it is found that even slight surfaceroughness may result in blotch- -iness or irregular darkening ofbackground areas. It is therefore preferred to grind or otherwise reducethe particle size of the ferric soap or equivalent component to minimumsize.

Another. means of improving the ability of the copypaper to formreproductions of colored originals is demonstrated in the followingexample.

' Parts by Example 2 weight Ferric stearate 100 Ethyl cellulose 61Teritiary-butyl catechol Triphenyl phosp 12 Acetone 1064 A smoothdispersion is formed as described in connection with Example 1, the soapcomponent being ground to minimum particle size; The mixture is coatedat 3 mils on a lightly plasticized 1 mil polyvinyl chloride film anddried at room temperature. The smooth glossy coating is opalescent. Itis next coated with a minimum transparentizing coating of liquidpolydimethylsiloxane (DC- 200" silicone liquid) by sponging with anexcess of the indicated; but other liquid and then removing the excessby rubbing with an absorbent towel. The surface is rendered transparentbut not greasy.

The copy-sheet thus treated is placed around the exposure cylinder ofthe apparatus described in Example 1. and a test sheet printed with avariety of colored inks is held with the printed surface inpressure-contact with the heat-sensitive coating. With the capacitorcharged at 2800 volts, the resulting irradiation causes darkening of theheatsensitive coating in areas corresponding to each of the inked areas,including black, blue, green, red, and yellow areas.

The printed original is then replaced by a receptor sheet of plain whitepaper and the flash repeated but at an initial voltage of about 3200volts. The previously darkened portions are substantially completelytransferred to the receptor sheet. The, background areas of thecopy-sheet are darkened but no transfer .foccursin these areas. Both theprinted original and the irjnage-coated receptor sheet are easilyseparated from the intermediate heat-sensitive copy-sheet.

, When thecopy-sheetof Example 1, or that of Example 2 priortoapplication of the silico'ne coating, is tested as,

above described, effective reproduction of the darker images isobtained, but'the lighter colors do not give cornple'te reproduction,and no legible reproduction whatever is produced at the yellow imagearea. Attempts to improve the reproduction of the lighter colored imagesby increasing the intensity of irradiation are not successful because ofexcessive background darkening.

Liqued silicone materials are effective in extremely small amounts andare presently preferred for the purpose mobile, heat-conductive,radiationtransmitting, void-filling liquids or pastes which are inerttoward the coatings and films with which employed and do not causesoftening or stickiness or other difficulties are likewise contemplated.These include fluorocarbon oils and, in some instances, lightpetroleumoils.

Resinous phenolic materials are known which are readily visibly reactivewith ferric soaps under the conditions described, and such materialshave been found useful both as reactants and at the same time asbinders, replacing the ethyl cellulose or other binder in whole or inpart.

Heat-sensitive coatings based on ferric-phenolic compositions have beenfound highly effective for the purpose of this invention and arepreferred; but other heat-sensitive coatings have also proven useful forthermographic reproduction and may be employed, as illus trated by thefollowing example.

The silver behenate is formed by precipitation from aqueous sodiumbehenate with one-half the molar quantity of silver nitrate added insolution sufficiently acidic to precipita-te the remainder of thebehenic acid.

The listed components are ground together in a ball mill to minimumparticle size. Separately there is prepared a solution of 25 parts ofprotocatechuic acid in 75 parts of acetone. Four parts of this solutionare then mixed with 20 parts of the dispersion to form the coatingcomposition. The latter is coated at a 3 mil orifice on 1 mil orientedpolyester film, dried, and overcoated with DC- silicon applied as a 20%solution in heptane by roll coating in an amount just sufficient totransparentize the initially opalescent surface.

The heat-sensitive film is pre-printed from a graphic original in theapparatus of Example 1 operated at a voltage of 2800, and the resultingimage transferred to parent image areas in an opaque background. vAssuch,

it can be employed for producing additional duplicates by photographicmeans, e.g. by light-sensitizing of blueprint paper through thetransparent areas followed by developing or intensifying with water orchemical solutions as required. Somewhat analogously, the reproductionsproduced on the paper receptor sheets may serve as graphic originals forthe preparation of further reproductions by thermographic or othermethods. In both instances, any desired number of duplicates can beproduced. A further means of providing duplicates is described in thefollowing example.

Example 4 Airecepto'r sheet is provided by coating the smooth,

clay-loaded and heavily calendered surface of a paper web with a thinlayer of polyvinyl alcohol, applied from aqueous solution. The resultingsurface is hydrophilic. Products of this character are commerciallyavailable, being used in the preparation of-Multilith lithographiccopysheet material. Areproduction of a printed graphic "original isproduced on the heat-sensitive copy-sheet of Example '1 by'thermographiccopying procedures, in this case by brief intense irradiation of theoriginal through the copysheet in pressure-contact therewith and withradiation obtained from an incandescent filament and concentrated at theprinted surface. a

The printed portions arenext transferred from the copy-sheet to thehydrophilic surface of the receptor sheet by methods as described underExample 1, using a voltage of 2500 in the specific. apparatus there de-Iscribed. There'is. provided an organophilic image pattern on ahydrophilic background. The'resulting sheet is then swabbed with aqueousfountain solution, and used for making multiple prints-with oil baseinks on plain paper by lithographic techniques commonly employed in vMultilith duplicating.

The successful reproduction of colored. originals requires close andcontinuous contact between original and heat-sensitive layer. Finegrinding of dispersed particles has been shown to be of assistance inthis respect, the :size

of voids between particles being thereby diminished. Improved contactbetween copy-surface and original may also be securedby' providing acompressible or conformable sub-layer' between heat-sensitive layer andtransparent support web. For example, a thin added layer of relativelysoft vinyl resin has been found to be of assistance; presumably theparticles of the heat sensitive layer are partially pressed into suchlayer under the pressure-contact between copy-sheet and original.Application of a mobile transparent filler material such as siliconeoil, as hereinbefore described, similarly reduces the size of surfacevoids and ensures more complete contact,

explanation for. this effect, is it suggested that, the transfer ofimage-forming material is accomplished by what amounts to volatilizationof such material, with subsequent condensation at and within the surfacepores of the contiguous receptor sheet, rather than by simple fusion andbulk transfer of molten material. In any event, and regardless oftheory, the sheet materials and processes 'here described have now madepossible the economical and rapid permanent reproduction of both,colored and black-on-white graphic originals on a wide variety ofreceptor surfaces by strictly thermographic techniques requiring nochemical or other image-development.

An additional advantageous feature of this invention, inherent in theforegoing examples, is the ability to intensify partial images formed atless than optimum irradiation by front-printing on heabsensitivecopy-paper. In Example 1 it is observed that the initially unaffectedbackground areas of the copy-paper are drastically darkened during thesecond irradiation which transfers the previously darkened image-formingportions to the receptor-sheet. Although the background areas show noobservable darkening during the initial irradiation, there is apparentlyproduced sufiicient change in these heatsensitive areas so that theybecome substantially more absorptive of the radiation. Subsequentirradiation then produces at least a moderate heating effectwithin'these background areas, resulting in the drastic darkeningobserved in such areas during transfer of the previously fully darkenedimage-forming areas. The phenomenon may be utilized in producing fullyvisible reproductions of graphic originals which cannot safely besubjected to the otherwise indicated high intensity of radiation. Forexample, irradiation of a black-on-white original through theheat-sensitive copy-paper is carried out at an intensity sufiicient toproduce only a barely visible darkening of the image areas. In theapparatus described in connection with Example 1, such an irradiationmight be accomplished by charging the capacitor to about 1500 volts orless, rather than to 2000-3000 volts as indicated in connection with.the example. The original is theri removed, and the copy-paper furtherirradiated with one or more additional Zfiashes at the indicated lowintensity. It is found that the differential in radiation absorptivitybetween the partially darkened image areas and the visibly unchangedbackground areas is sufficient under these conditions to result inmaximum darkening of the image areas with substantially no visiblechange in the background areas. The resulting intermediate is thenemployed in forming a reproduction on plain white paper or otherreceptor-sheet by further flash irradiation at required high intensityashercinbefore described.

-In the accompanying drawing, FIGURE 1 is a schematic representation, incross-section, of the apparatus described in connection with Example 1;FIGURES 2, 3 and 4 are fragmentary views showing the progress of thereproduction process; and FIGURES S and 6 are representations ofportions of alternative forms of heat-sensitive copy-sheets.

In FIGURE 1, a copy-sheet 12 and an original 13. are held in positionagainst a transparent cylinder 11 by means of an outer fabric cover 14.Irradiation issupplied from flash tube 10 through the cylinder 11 andthe copy-sheet :12 to the differentially radiation-absorptive graphicoriginal 13. As illustrated in more detail in FIGURE 2, the heatingefiect thus produced at the radiation-absorptive image areas 15 of theoriginal 13 causes a darkening at corresponding areas 16 ofthe'heat-sensitive layer 17 of the copy-sheet 12. The visibly darkenedareas 16 are radiation-absorptive. The remaining areas of theheat-sensitive layer 17 remain essentially visibly unchanged.

Where the radiation absorptivity of the areas 16 is inadequate orundesirably low, the copy-sheet may be subjected to the application offurther radiation suflicient to cause substantially complete darkeningof the image-producing areas 16, as illustrated in FIGURE 3, withoutmaking any significant or objectionable change in the remaining areas ofthe heat-sensitive layer 17. In most cases, this intermediate step isunnecessary.

As illustrated in the exploded view of FIGURE 4, the original 13 is nextreplaced by a sheet of plain white paper 18, 01' other receptor sheet,and the composite again subjected to fiash irradiation. Theradiation-absorptive image-reproducing areas 16 are transferred from thecopy-sheet 12 to the receptor sheet .18, producing a permanentreproduction of the graphic original. The remaining heat-sensitive areasof the layer 17 of the copysheet 12 are at the same time partiallydarkened, the

copy-sheet thereby forming a negative transparency cor-' original,comprising (1) exposing the original to brief intense irradiationthrough a radiation-transmitting heatsensitive copy-sheet inheat-conductive contact with said original for producing in saidcopy-sheet a radiation-absorptive and visibly distinct image portioncorresponding to the radiation-absorptive image-forming area of saidoriginal, and (2) exposing the thus converted copy-sheet to furtherbrief irradiation at an intensity at least equal to that used in (1)while holding the copy-sheet with its heat-sensitive surface in intimatecontact with the receptor sheet surface, for selectively transferringsaid visibly distinct image portion permanently onto the receptor sheetsurface, said copy-sheet consisting essentially of aradiation-transmissive base sheet and a visibly heat-sensitiveradiation-transmissive coating thereon, 'said coating being renderedvisibly distinct and radiation-absorbent on being briefly heated in thethermographic copying process, the thus heated portions being readilytransferable from said'base sheet on heating to substantially highertemperature. I

2. The method of preparing the surface of a hydrophilie printing-platefor lithographic printing of reproductions of a graphic original,comprising (1) exposing said graphic original to brief intenseirradiation through a radiation-transmitting copy-sheet having an'organophilic visibly heat-sensitive layer in heat-conductive contactwith said original for producing in said layer a'radiationabsorptive andvisibly distinct image portion corresponding to the radiation-absorptiveimage-forming area of said original, and (2) exposing the thusconvertedcopy-sheet to further brief irradiation at an intensity atleast equal to that used in (I) while holding the copy-sheet with itsorganophilic layer in intimate contact with said printingplate surface,for selectively transferring the organophilic image portion to thehydrophilic printing-plate surface; said copy-sheet being furthercharacterized as consisting essentially of a radiation-transmissive basesheet and a visibly heat-sensitive organophilic radiation-transmissivecoating thereon, said coating being rendered visibly distinct andradiation-absorptive on being brefly heated to conversion temperature inthe thermographic copying process, the thus converted portions beingreadily transfcrable from said base sheet on heating to a temperaturesubstantially higher than said conversion temperature.

3. The method of making a thermographic reproduction, on a receptorsheet having a surface, of a graphic original, comprising (1) exposingthe original to brief intense irradiation through aradiation-transmitting heatsensitive copy-sheet in heat-conductivecontact with said original for producing in said copy-sheet aradiation-absorptive and visibly distinct image portion corresponding tothe radiation-absorptive image-forming area of said original and at'lessthan maximum image density while avoiding any visible change in thebackground portion, (2) exposing the partially converted copy-sheet tofurther brief intense irradiation sufficient to increase the density ofthe partially radiation-absorptive image area: while avoiding anysignificant discoloration of said background, and (3) exposing the thusconverted copy-sheet to further brief irradiation at an intensity atleast equal to that used in 1) while holding the copy-sheet with itsheat-sensitive surface in intimate contact with the receptor sheetsurface, forselectively transferring said vissibly distinct imageportion permanently onto the receptor sheet surface; said copy-sheetbeing further characterized as consisting essentially of aradiation-transmissive base sheet and a visibly heat-sensitiveradiationtransmissive coating thereon, said coating being renderedvisibly distinct and radiation-absorptive on being briefly heated toconversionvtemperature in the thermographic copying process, the thusconverted portions being readily transferable from said base sheet onheating to a temperature substantially higher than said conversiontemperature.

References Cited in the file of this patent UNITED STATES PATENTS2,503,758 Murray Apr. 11, 1950 2,616,961 Groak Nov. 4, 1952 2,663,654Miller et a1. Dec. 22, 1953 2,663,655 Miller et a]. Dec. 22, 19532,749,253 Shoemaker et al. June 5, 1956 2,764,085 Shoemaker et al Sept.25, 1956 2,769,391 Roshkind Nov. 6, 1956 2,800,077 Marron July 23, 19572,808,777 Roshkind Oct. 8, 1957 2,813,043 Clark Nov. 12, 1957 2,859,351Clark et al Nov. 4, 1958 2,910,377 Owen Oct. 27, 1959 2,916,395 OwenDec. 8. 1959 2,919,349 K'uhrmeyer et al. Dec. 29, 1959

2. THE METHOD OF PREPARING THE SURFACE OF A HYDROPHILIC PRINTING-PLATEFOR LITHOGRAPHIC PRINTING OF REPRODUCTIONS OF A GRAPHIC ORIGINAL,COMPRISING (1) EXPOSING SAID GRAPHIC ORIGINAL TO BRIEF INTENSEIRRADIATION THROUGH A RADIATION-TRANSMITTING COPY-SHEET HAVING ANORGANOPHILIC VISIBLY HEAT-SENSITIVE LAYER IN HEAT-CONDUCTIVE CONTACTWITH SAID ORIGINAL FOR PRODUCING IN SAID LAYER A RADIATIONABSORPTIVE ANDVISIBLY DISTINCT IMAGE PORTION CORRESPONDING TO THE RADIATION-ABSORPTIVEIMAGE-FORMING AREA OF SAID ORIGINAL, AND (2) EXPOSING THE THUS CONVERTEDCOPY-SHEET TO FURTHER BRIEF IRRADIATION AT AN INTENSITY AT LEAST EQUALTO THAT USED IN (1) WHILE HOLDING THE COPY-SHEET WITH ITS ORGANOPHILICLAYER IN INTIMATE CONTACT WITH SAID PRINTINGPLATE SURFACE, FORSELECTIVELY TRANSFERRING THE ORGANOPHILIC IMAGE PORTION TO THEHYDROPHILIC PRINTING-PLATE SURFACE; SAID COPY-SHEET BEING FURTHERCHARACTERIZED AS CONSISTING ESSENTIALLY OF A RADIATION-TRANSMISSIVE BASESHEET AND A VISIBLY HEAT-SENSITIVE ORGANOPHILIC RADIATION-TRANSMISSIVECOATING THEREON, SAID COATING BEING RENDERED VISIBLY DISTINCT ANDRADIATION-ABSORPTIVE ON BEING BREFLY HEATED TO CONVERSION TEMPERATURE INTHE THERMOGRAPHIC COPYING PROCESS, THE THUS CONVERTED PORTIONS BEINGREADILY TRANSFERABLY FROM SAID BASE SHEET ON HEATING TO A TEMPERATURESUBSTANTIALLY HIGHER THAN SAID CONVERSION TEMPERATURE.